For producing high resolution patterns in materials using cost effective methods, procedures of patterning involving the contact of a master pattern into resist have shown promise and practical application, which include nanoimprint lithography as described in U.S. Pat. Nos. 5,772,905 and 6,719,915. In this approach, a topographical relief pattern on a master, which is made of polymer or a hard material like quartz or silicon, is pressed into a polymer film on a substrate, which is then the polymer film is cured, and the master retracted after from the polymer film to reveal the pattern. While the technique has advantage in simplicity and high resolution, its disadvantages include the defects and lowered yields generated from the separation of the master from the polymer film that can fracture the material during the separation process or otherwise contaminate the master. In addition, the separation step and reloading of the master for the next substrate lowers the throughput for the approach to nanoimprint lithography. Because the material needs to be curable when fully encased by the master, it is not possible to pattern materials that contain solvents requiring interaction with the environment in order to evaporate during the patterning process.
To provide a solution to these problems, molecular transfer lithography (MxL) as described in U.S. Pat. No. 6,849,558 is a technique in which a dissolvable template made of polyvinyl alcohol (PVA) as described in U.S. Pat. No. 7,345,002 is used to produce patterns that involve the adhesion onto substrates of functional materials coated on patterned PVA templates, followed by the dissolution of the PVA template to leave the patterned material on the substrate. The PVA template is formed by first casting a PVA-based solution on a master substrate that has a topographical pattern produced by means such as photolithography or electron beam lithography; and then from the master removing the dried PVA film, which yields a template with a relief pattern of an image inverse to that of the master.
Of MxL and PVA templates, the innovation is a materials transfer printing that couples water-dissolvable, ultra-high resolution templates coated with functional materials including polymers that are pre-processed while on the templates prior to transfer onto substrates that include silicon, plastic and glass. The materials transfer printing process employing dissolvable templates enables a unique way to form high resolution patterns and has several advantages over alternative methods like nanoimprint lithography, embossing or soft lithography, including: (1) a conformal template for patterning over significant variations in substrate flatness, (2) a large-area patterning capability because it dissolves away eliminating frictional effects from physical separation, or step-and-repeat and stitching complications, (3) a material transfer process by which the template is coated due to compatible surface tension that enables thin residual layers and eliminates the fluidic displacement challenges of imprinting, (4) eliminates defect propagation problem of contact printing through the use of a dissolvable one-time-per-use disposable template, (5) a solution to the “demolding” defect generation problem of contact printing by elimination of that step, (6) ability to work with masters from a variety of materials including opaque materials like silicon, (7) coating the template rather than the substrate provides access to the interfacial layer prior to bonding, enabling secondary processing steps, (8) fewer steps than imprint lithography at the fabrication site, since it eliminates the need to coat the material on the substrate because the water-soluble template is pre-coated with a dried, cured resist, (9) apparently very little or zero interfacial mixing between the water-soluble template and the functional materials of interest based on the high resolution results, (10) ultra-high resolution, polymeric template to 25 nm and lower, (11) potential for high Young's modulus with complete drying relative to elastomeric materials, (12) ultra-high aspect ratios to at least 5:1 because of the water dissolution nature of the template, (13) low-cost materials which enables a consumable approach to patterning, (14) fast drying times in forming a replicated template involving simple spin-coating methods, (15) is water-dissolvable thereby making for an environmentally friendly approach to nanopatterning, as well as reducing the costs and hazards associated with materials handling and disposal, (16) works well with solvent containing materials because the solvent can be evaporated after coating to achieve pattern formation prior to transfer, thereby eliminating the need to deform a solid thin film in an alternative embossing scheme, (17) although the template dissolves in water, it does not dissolve in organic solvents and can therefore be coated, (18) the surface energy of the template permits coating of materials onto the template using spin-coating methods, whereas other template surfaces are too slippery to permit the materials on the surface, (19) ability to vacuum deposit metallic materials onto the template prior to transfer printing onto substrates, thereby eliminating etching for products whether on plastic or glass.
To automate the transfer of materials from the template to the substrate for Molecular Transfer Lithography, the tool must perform the adhesion operation without introducing voids or entrapping air bubbles. While it is possible to retrofit imprint tools or contact photolithography tools, which are designed to maintain hold of the master or mask during the patterning process, such tools use rigid backs to perform the contact, which would prevent the conformal contact of dissolvable template to the substrate. Because the imprint tools are designed to hold onto the master or mask, it is time consuming to load a new template into such a system, which would be the case for the MxL procedure, and therefore the yield would decrease. It is possible to load the template onto the wafer, and then move both into the chamber, but contacting the template onto the substrate before bonding can lead to air inclusions or partial bonding before the adhesion process begins.